The present invention pertains to a battery, a novel iron-sulphide-based anode suitable for use in said battery, methods for producing said anode and battery, and use of said battery.
Around 1970 nickel-iron batteries competed with lead-acid for a larger market share. They were favorable because of their longer lifetime and their safe alkaline electrolyte. The anode material was metallic iron, mostly sintered or pressed where iron and iron oxides were mixed. However, the nature of the metallic iron and nickel hydroxide electrode causes low energy efficiency, high self-discharge, bad high discharge characteristics and gassing problems. The sintering and/or annealing process led to high manufacturing cost. As a result, nickel-iron batteries got displaced by other types (especially lead-acid) in almost all applications.
At present, the lead-acid battery is one of the market leaders in the battery field, with the main advantages being low cost and low maintenance. However, the short lifetime, failure on deep and high rate discharges and it holding hazardous materials make it unfavorable for stationary applications, e.g. on-grid peak shaving or off-grid energy systems with a lifetime of up to 20 years.
Another development in the battery field was a focus on light batteries for laptops and electric vehicles. Lithium-ion batteries gained interest due to their low weight and high energy density. However, Li-ion batteries suffer from lifetime issues and high production cost, and are therefore not very suitable for stationary applications.
In stationary applications, weight is not a primary issue. The ideal stationary battery has a lifetime of 20 years at daily charge/discharge cycles, has a good energy cycling efficiency, is capable of supplying peak loads and deep discharges, is robust and uses environmental benign and available materials. The need for this battery is eminent, both for off-grid systems and on-grid peak shaving applications. The present invention provides such a battery with a novel realisation of the anode based on iron sulphide.
The battery according to the invention comprises an anode comprising iron sulphide as active material, with the sulphur content being at least 5 wt. % of the total of iron and sulphur, a cathode, and an alkaline electrolyte comprising an alkaline component dissolved in water, with the anode comprising less than 50 wt. % of other active materials than iron sulphide.
It has been found that the use of iron sulphide in the anode provides a rechargeable electrical energy storage system which is low-cost, easy to produce, and environmental friendly, and which shows a long lifetime and has excellent electrochemical properties like high power density and good cycling efficiency. The battery according to the invention also shows superior charge/discharge behavior as compared to e.g. lead-acid and nickel-iron batteries.
It is noted that sulphur (e.g. in the form of ferrous sulphide) has been used as an additive in the iron electrode of conventional nickel-iron batteries, to accomplish the initial activation and add defects in the electrode that increase bulk conductivity. However, the amount of sulphur added was reported to be required to be below 1 wt. %, because higher sulphur contents were considered undesirable. For example, GB 1359746 indicates that a sulphur content in excess of about 0.03 wt. % S had very undesired effects on the battery.
It is also noted that iron sulphide is sometimes used in the cathode of anhydrous lithium ion batteries, where it is used to intercalate lithium and ultimately form Li2S and Fe upon discharge. This is of course different from the present invention, where the iron sulphide is used in the anode in an aqueous alkaline battery and not as cathode of an anhydrous lithium battery.
Further, Bong-Chull Kim et al. (Solid State Ionics 176 (2005) 2383-2387) describes an all solid state Li-secondary battery with FeS anode. These solid-state Li-ion batteries also use the intercalating effect of Lithium in FeS and therefore are fundamentally different from batteries based on aqueous alkaline electrolyte like that of the present invention.